Simulation And Analysis Of Fluid Structure Interaction For Impeller Of Hydrodynamic Coupling

Hydrodynamic coupling is a kind of transmission element, using the liquid as themedium. It is widely used in industries, such as, metallurgy, mining, powergeneration, cement, petrochemical, textile, shipping, and the economic benefits isobvious. Especially the energy saving effect of variable speed hydrodynamic couplingin these fields is evident. With the development of the modern industrial machinery tohigh speed, high-power direction, the development of variable speed hydrodynamiccoupling and hydrodynamic transmission equipment also promote to the relativedirection. Based on the market demand and the development of related technology, aswell as people's understanding of hydrodynamic coupling have been deepened, thehydrodynamic coupling will be more and more widely applied to high-power, highenergy-dissipative equipment in future. When high-power hydrodynamic coupling isworking, the impeller must stand enormous centrifugal force and fluid pressure, andthe impeller of hydrodynamic coupling is the key components of transfer power. Onceit breaks, it will directly damage the axletree, and as a result, the pump or the fan willnot work, so it's easy to threaten the safety of the normal operation for hydrodynamicunits, resulting in the whole machine invalidation. Because of that, we should payenough attention. When it is at speed, the impact of liquid on the blades ofhydrodynamic coupling will have a vibration, and if the vibration last a long time, itmay lead to structural fatigue, and the dynamic stress caused by vibration becomes animportant reason which results in blade cracks. Therefore, the strength of the impellerand blades are the key issues of high-power, high speed hydrodynamic coupling. Inthe machinery, such as, Hydrodynamic coupling, Compressor, Turbo machine,Hydraulic turbine, and so on, unsteady flow of the gas or the liquid will put a unsteadyforce to blades, which makes the blades have a vibration or deformation. The vibrationor deformation of blades in turn acts on the fluid field, which changes the unsteadydegree of fluid field. This is a typical characteristic of the gas-solid and liquid-solidinteraction vibration. Because the vibration problem of impeller under viscous flow isa very complex nonlinear dynamic problem of the multi-field coupling, so far, it has been a difficult problem to simulate the real inherent mechanism of fluid structureinteraction and vibration. On a basis of the theory of the fluid mechanics and fluiddynamics, and according to the finite element method as theoretical guidance, thispaper is using the numerical simulation and making an analysis of fluid structureinteraction for impeller of hydrodynamic coupling and fluid use the weak-couplingmethod, and adopting indirect coupling methods to achieve the coupling process tostudy the influence of hydrodynamic coupling's performance for fluid structureinteraction. The result of numerical simulation provides a reference for the design ofthe hydrodynamic coupling in future. It is significant to shorten the design cycle,reduce design risk, improve and enhance the performance of hydrodynamic coupling.Based on the fluid structure interaction of YOCQZ450 model hydrodynamiccoupling, this paper makes a research on the following several aspects:(1) A detailed comparative analysis is done to the existing calculation method andcalculation model for fluid structure interaction, such as, finite element method (FEM),finite volume method (FVM) and so on, then the appropriate numerical simulationalgorithm for fluid structure interaction is chosen;(2) The three-dimensional modeling software is used to set up 3D geometricmodel and flow model of impeller of hydrodynamic coupling, then the solid model ismeshed. According to the actual working condition of hydrodynamic coupling, it setsthe boundary conditions; based on the Navier-Stokes equations and standard k ?εturbulence model, the fluid mesh model is imported to the fluid analysis software, andthe inner flow field of hydrodynamic coupling is calculated. The inner real flowsituation and the irregular flow of hydrodynamic coupling is understood deeply, theflow characteristics of distribution in different working situation and different quantityof liquid are achieved after numerical simulation, it provides the foundation for theresearch of fluid structure interaction for impeller of hydrodynamic coupling.(3) Based on the three-dimensional flow field calculation, the mesh model ofimpeller and blades are imported into the finite element analysis software. UsingAPDL language with least error, the pressure of blades'surface is loaded onto themodel in finite element software. Considering the different characteristics of theworking situation, the deformation and stress distribution of impeller and blades areachieved under the impact fluid and centrifugal force. After comparing with the stressdistribution of blades in different working situation, the research shows that the maximum equivalent stress is observed at these areas: the joint of interface and outletof blade, the joint of interface and top of blade. The stress gradient at these areas isquite large, and the stress concentration is evident, which tends to cause fatigue failure.Compared with the deformation of blades in different working situation, we found thatthe biggest deformation part of blades is in the middle of blades and the furthest placesaway from the roots. Compared with the position of the maximum equivalent stress indifferent working situation, we find that the stress of hydrodynamic coupling bladechanges greatly with the changes of quantity of liquid.(4) After finite element analysis is transferred to the modeling software, newblade model and the calculation spaces of fluid is reconstructed by using the distortionstructure. Then, the new model is meshed, and the fluid mesh model is imported intofluid analysis software, at last, the inner flow field of hydrodynamic coupling iscalculated after deformation, observing the disturbance of flow field after deformationof the blades, finally, we achieve the FSI purpose. Comparing with distribution offlow field, the results show that the blade distortion has great effects on the pressurefield of the blade, and the average stress increases markedly in whole flow field. It isprobably the main reason for blade fracture, so that blades longevity expectancydecreases. It is harmful for the stable operation of the hydrodynamic coupling.(5) The influence on fluid structure interaction for the performance ofhydrodynamic coupling is researched at a starting level, and the result of numericalsimulation provides a reference for the design of the hydrodynamic coupling in future.It is significant to shorten the design cycle, reduce design risk, improve and enhancethe performance of hydrodynamic coupling. It establishes the foundation for furtheranalysis and accurate understanding the internal flow of hydrodynamic coupling, andprovides substantial scientific data and the theoretical basis for depth study of fluidsolidinteraction of hydrodynamic coupling; it is an important theoretical significanceto reveal coupling mechanism of hydrodynamic coupling.